If gases or liquids containing solids are to be closed off fluid-tight under a considerable pressure difference, as is necessary, for example, at the fill openings of pressure containers for pneumatic pressure conveyors, a valve with a high-quality gas and liquid-tight construction of the valve disk and of the valve seat must be used, which usually requires surfaces and work materials which are exposed to wear. When such valves are closed, high flow speeds which cause heavy wear can occur at the sealing surfaces. Particles can also be enclosed between the cooperating pressure surfaces of valve disk and valve seat and destroy the surfaces under the force of closure. In order to avoid this, an auxiliay closing part is put in front of the fluid-tight valve which is essentially solid-tight or at least retains coarse solids such that the valve can be closed in a protected manner at a low flow speed and in the absence of solids or at least of coarse solid particles. Such an arrangement consisting of a valve and an auxiliary closing part is complicated.
The invention therefore has the task of reducing the space requirements and the expense of construction.